Project Abstract Washington, DC has approximately 13,000 people living with HIV (PLWH) and is one of the HIV ?hotspots? in the US that collectively contribute to 50% of new HIV diagnoses. As we strive to end the HIV epidemic, the ability to characterize persons who are newly diagnosed with HIV, effectively direct treatment efforts for HIV and its co-occurring conditions, and use novel prevention tools to avert further transmissions, are of critical importance. The DC Cohort, a longitudinal cohort study of over 10,000 PLWH receiving care at 15 clinical sites in DC, is uniquely positioned to help end the HIV epidemic. The Cohort was launched in 2011 with the goal of bending the trajectory of the HIV epidemic in DC by improving the quality of care. The Cohort engages academic and community-based clinics, links to DC Health Department (DOH) databases, and provides near real-time performance feedback to clinics on HIV outcomes using a data visualization Clinical Dashboard. All of this is achieved through automated data extraction and harmonization of electronic medical records data from varied clinical settings and all age groups. The Cohort provides a representative, population-level and scientifically productive research resource that does not exist in most urban high prevalence cities. Building off the Cohort?s infrastructure and achievements, we will expand this robust population-level data repository to comprehensively and longitudinally track outcomes among PLWH in a high prevalence city. We will incorporate new data sources into the Cohort including administrative, service, pharmacy, additional co-morbidity and patient-reported outcomes data. Access to multi-level data will enhance the monitoring of HIV and co- morbidities outcomes. Next, we propose to use the Cohort to monitor the impact and effectiveness of Ending the HIV Epidemic (EHE) initiatives in DC and contribute lessons learned to national EHE efforts. The Dashboard will monitor key EHE indicators: retention in care; viral suppression (VS); availability, initiation and efficacy of new ARV therapeutics; and reductions in health disparities. With this tool, local HIV providers and the DC DOH can support those at greatest risk for suboptimal outcomes. Finally, we will use the Cohort to develop pioneering interventions to improve the quality of care among PLWH. We will partner with the DC Center for AIDS Research, local and national HIV investigators, and community stakeholders to identify and develop clinical, epidemiologic, socio-behavioral, basic science, and implementation science interventions to improve care. We will use the Cohort infrastructure to identify potential participants and clinical sites for these studies in support of NIH-funded and other research proposals. The goals of the Cohort align with OAR, NIAID, and EHE priorities which focus on reducing health disparities, achieving VS, monitoring quality of care, and improving the management of HIV-related clinical outcomes. The DC Cohort is an unparalleled clinical, research, and public health resource which enables us to monitor care in a high prevalence city. Lessons learned will produce generalizable knowledge that can be applied in other urban hotspots across the US.